1. Field of the Invention
This invention relates to a torque steering angle sensor, which is capable of detecting a steering torque and a steering angle of a steering wheel of a vehicle.
2. Description of the Related Art
Conventionally, electrically assisted power steering devices for vehicles are provided with a torque sensor to be able to detect a steering torque. Such a torque sensor is able to detect a steering angle as well as the steering torque. See, e.g. JP-A-2010-190632.
A torque sensor disclosed by JP-A-2010-190632 as a first embodiment includes a torsion bar for coupling together an input shaft and an output shaft of a steering shaft, a sensor yoke assembly, which is fixed to the input shaft of the steering shaft, a magnetic flux collecting yoke assembly to collect the magnetic flux of the sensor yoke assembly, an annular permanent magnet, which is rotated together with the output shaft of the steering shaft, a first magnetic field detector, which is disposed between a first magnetic flux collecting yoke constituting portion and a second magnetic flux collecting yoke constituting portion which constitute the magnetic flux collecting yoke assembly, and a second magnetic field detector, which is arranged opposite an outer circumferential surface of the permanent magnet.
The torque sensor is configured in such a manner that the steering torque is detectable from a variation in magnetic field strength detected by the first magnetic field detector depending on a torsional angle of the torsion bar. Also, a rotational angle between adjacent N and S poles is detectable from a variation in magnetic field strength detected by the second magnetic field detector resulting from rotation of the permanent magnet, and the steering angle can be computed by cumulating the rotational angles.
In addition, a torque sensor disclosed by JP-A-2010-190632 as a second embodiment, the outer circumferential surface of the permanent magnet is two pole parallel magnetized, so that the second magnetic field detector is able to detect a magnetic field direction. This allows for more easily computing the steered angle, as compared to the torque sensor in the first embodiment.
Further, a torque sensor disclosed by JP-A-2010-190632 as a third embodiment includes, in addition to each constituent element of the torque sensor of the first embodiment, a first gear, which is fixed to a lower surface of the permanent magnet, a second gear, which meshes with the first gear, a two-pole magnet, which is fixed to the second gear, and a third magnetic field detector, which is arranged opposite the two-pole magnet. The first gear and the second gear are both made of spur gears having different numbers of teeth. This torque sensor is able to detect an absolute value of the steering angle, in other words, an absolute angle, from a combination of a magnetic field strength detected by the second magnetic field detector and a magnetic field strength detected by the third magnetic field detector, even when the steering shaft is multi-rotated.